The present invention relates to an improvement of position error correction equipment which corrects an error in the position of movement relative to a commanded position in a numerical control machine tool through using error correction data prestored in an error storage circuit.
In a numerical control machine tool in which commanded position information is compared with detected position information from a position detector mounted on a servomotor shaft or ball screw for moving a movable machine part and in which position control is carried out by driving a servomotor, so that an error between the commanded and detected position information may be reduced to zero, the position control accuracy is dependent substantially on the accuracy of the ball screw and other gear mechanisms. When requiring highly accurate position control, there have heretofore been adopted various position error correcting methods, such as a backlash correction, pitch error correction or the like in a mechanical system; in the past, however, since the correction has been effected based on only fixed error correction data, that is, correction data predetermined for one state of the machine tool, for example, a constant temperature of a ball screw and a constant weight of a movable part, accurate correction has not always been carried out. The reason is that, for instance, a pitch error of the ball screw may cometimes undergo a large variation due to a temperature change or the like of the ball screw, and the quantity of backlash in the mechanical system may greatly change with the change in the weight of different workpieces.